You know whats funny, I stopped using Chrome and use Firefox now because Firefox is so much faster. The exact same reason I switched to Chrome 5 years ago. Also I'm slightly less creeped out.
I think this is pretty common. In fact, this can happen even if neither browser changes at all. Your profile builds up and your history searches etc. slow down, so you switch browsers and get a clean profile to start with. Repeat. (I'm not saying that that is what you are experiencing, but I think it's a factor for every browser user.)
